Light source assembly and methods for aircraft external lighting

ABSTRACT

An aircraft light assembly comprises a light apparatus configured to be supported in a space on the body of an aircraft. The apparatus has one or more light emitting diodes ( 13 ) generating visible light and an outer structure overlying the LEDs. The outer structure includes a light transmission portion through which visible light from the LEDs can pass, and a metallic portion with an outer surface exposed to the external airflow. A heat-transmitting connection thermally links the LEDs to the metallic portion so that heat from the LEDs flows to the outer surface and is dissipated to the external airflow. The light assembly is configured to be secured in a conventional socket for an incandescent navigation light bulb and to receive the electrical current supplied thereto by the aircraft electrical system. Civilian applications of the unit have only visible LEDs. When the unit is for a military aircraft, it has electric circuitry connected with a visible light source and an IR light source, and the electric circuitry is configured to process the input current from the socket and based thereon operate in either a visible mode or covert IR mode. Where the current is in one electrical state, such as for example a certain voltage, the electric circuit sends power only to the visible light source. When the current is in a different electrical state, e.g., a different voltage level, the circuitry sends power only to the IR source, and no visible light is emitted. Different input current voltages or characteristics are also used to cause the IR emitter to flash in various patterns that can be programmed into the unit. All control may be accomplished over a single pair of wires, as in existing systems that do not have IR mode capability. To upgrade existing aircraft, light source units a shaped to fit in the apertures for existing lenses over incandescent navigational fixtures.

This application is a national phase application under 35 U.S.C. 371claiming the benefit of PCT/US03/04290 filed on Feb. 13, 2003 acontinuation-in-part of U.S. patent application Ser. No. 09/665,600entitled DUAL MODE LIGHT SOURCE FOR AIRCRAFT EXTERNAL LIGHTING filed onSep. 19, 2000 by inventors John J. Martin and Cary H. Leach, whichissued as U.S. Pat. No. 6,559,777 B1 on May 6, 2003 and is a CIP of60/356,854 filed on Feb. 13, 2002 and herein incorporated by reference.

FIELD OF THE INVENTION

This invention relates to navigation light sources provided for aircraftthat are used to render the aircraft visible, and more particularly tonavigation lights for civilian or military aircraft that use lightemitting diodes (LEDs) to generate visible light. The invention alsorelates to apparatus and methods of upgrading the navigation lights ofexisting aircraft.

BACKGROUND OF THE INVENTION

The aviation authorities of many countries require that commercialaircraft, and also military aircraft, when in civilian airspace onnon-covert activities, have navigational lighting to improve theirvisibility at night. Under U.S. regulations, when any aircraft (militaryor civilian) is flown during darkness in unrestricted airspace or in amilitary operations area (MOA), the external lighting of the aircraftmust conform to FAA requirements for chromaticity (‘color’), luminousintensity (‘brightness’), and angular coverage. Generally, thenavigation lighting comprises red lights on the left side and greenlights on the right side of the plane, and this external lightingnormally is provided by incandescent light bulbs in sockets on theoutside of the plane, conventionally powered by electricity from theinternal electronics of the aircraft.

The lifetime of incandescent lamps, especially in military aircraftexterior lighting applications, is limited, and replacement ofincandescent lamps in the exterior lighting fixtures of vehicles, inparticular aircraft, is a frequent maintenance task. For example,interviews of squadron maintenance personnel indicate that the averagelifetime of incandescent lamps in the main left and right navigationlight fixtures in F-16 aircraft is approximately 75 hours. A means ofincreasing the reliability of exterior light sources while maintaininglevels of luminous intensity required to meet Federal AviationAdministration (FAA) regulations is therefore needed.

Compared to conventional incandescent lamps, light emitting diodes(LEDs) contain no filaments and can theoretically provide lifetimesmeasured in thousands of hours. Also, LEDs are far more efficient inconverting electrical energy into light energy. However, LEDs are notperfect converters of electrical energy into light energy, and someenergy always will be lost as waste heat.

This creates a problem for possible use of LEDs in aircraft navigationlighting, because the heat created increases the temperature of theLEDs, and, for a given drive voltage, the hotter an LED gets, the lesslight that LED emits. The problem is even greater in the area ofnavigation light aviation applications, because to achieve luminousintensity levels conforming to FAA/ICAO regulations a number of highintensity LED diodes (individual light emitters) must be integrated andco-packaged. However, the added LEDs generate substantial heat, whichelevates the temperature of the LEDs. This elevated temperature in turntends to reduce the intensity of the light. Sufficiently hightemperatures will ultimately degrade the LEDs so that they either go outentirely, or function at a greatly reduced illumination level. Use ofLEDs in aircraft light systems is consequently subject to problems ofoverheating.

As mentioned above, military aircraft are required to have visiblenavigation lights similar to those of civilian and commercial aircraft.When flying a wartime night mission or night training sortie, a militaryaircraft may transit through unrestricted airspace in which civilianaircraft also operate, and it must have aircraft external lighting thatconforms to FAA requirements during this transit. However, during nightflight operations in wartime conditions, or during night flight trainingin restricted airspace, aircraft external lighting that is visible tothe unaided eye is undesirable.

For military aircraft in covert activities or other military situationswhere visibility would be a disadvantage, one approach was for the pilotof the military aircraft to simply turn off the external lighting. Thepilot can adjust the intensity of the navigation lights, or turn themoff completely, with a brightness control dial in the cockpit hat variesthe voltage of the AC current sent to the light socket.

In recent years, however, it has been noted that, in covert activities,while the aircraft was not visible to the enemy, it was also not visibleto friendly aircraft, and planes began to be supplied with covert modeIR light sources in addition to the visible navigational lights. Incovert operation, only emissions in the near-infrared of appropriateintensity are used, and visible navigation light is not emitted. The IRlight emitted is not visible to the unaided human eye, but can be seenwith appropriate viewing equipment, e.g., night vision goggles (NVGs)that are utilized during night operations in many military aircraft,which are very sensitive to the deep red and near-infrared region of thespectrum.

To upgrade to covert IR capability making military aircraft externallighting to be selectable between visible and covert modes at willduring flight, IR light sources have ordinarily been additional arraysof IR diodes added to the outside of the plane in addition to theexisting navigational lights. Alternatively, filters have been mountedover the existing navigational lights and IR diodes mounted in the lightbulb fixtures. These kinds of additions, however, require substantialstructural work to create the mounts and to wire the new fixtures intothe aircraft body, which usually does not have very much extra room formore wiring. In addition, the extensive modifications result inconsiderable expense for an upgrade to covert IR capability.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide anavigation light for aircraft that makes use of LEDs, but that avoidsthe heat-related problems of the prior art.

It is further an object of the invention to provide an LED light sourcethat efficiently carries heat away from the LED source and radiates theheat to the environment outside of the aircraft.

It is also an object to provide such a system in a modular design thataffords easy replacement of the lighting assembly, and also provides arelatively easy upgrade from existing navigation lights to the improvedsystem, especially as an upgrade that does not require modification tothe existing aircraft structure.

According to the invention, an aircraft light assembly is provided foran aircraft having a body with an outer surface exposed to an externalairflow. The assembly comprises a light apparatus configured to besupported on the body of the aircraft and including one or more lightemitting diodes generating visible light. The apparatus also includes anouter structure overlying the light apparatus. The Outer structureincludes a light transmission portion through which visible light fromthe LEDs can pass, and a metallic portion with an outer surface exposedto the external airflow. The metallic portion secures the lighttransmission portion on the aircraft. A heat-transmitting connectionthermally links the LEDs to the metallic portion so that heat from theLEDs flows to the outer surface and is dissipated to the externalairflow.

Preferably, the outer surface of the metallic portion and the lighttransmission portion are configured so that the outer surface thereof isconformal to the outer contour of the aircraft body, at least on oneedge, e.g. the leading edge of the assembly.

It is further an object of the invention to provide a method forinstalling an LED-based aircraft light assembly.

It is further an object of the invention to provide for a dual modevisible and infra-red aircraft light source for military aircraft thatavoids the heat-related problems of the prior art.

It is also an object of the invention to provide a dual mode lightsource that provides for different flashing patterns of the infra-redemitter when in covert mode. Preferably, the different flash patternsare pre-programmable and selectable by existing controls withoutmodification to the electronics of the aircraft.

It is also an object of the invention to provide an aircraft lightingsystem that can function both as a visible navigational light system andalso as a covert IR light system for friendly eyes only. It is also anobject of the invention to provide a design and method that allows forrelatively easy upgrade of existing visible navigation lights to give anexisting aircraft IR covert capability without the need for anysubstantial mechanical adaptation of the plane's structure.

These and other objectives are accomplished by providing according to anaspect of the invention a dual mode light source unit configured so thatit can be secured into a conventional incandescent bulb socket on theaircraft. The light source has a connector portion that fits in thesocket and receives the electrical current supplied thereto by theaircraft electrical system. The unit also comprises electric circuitryconnected with the connector portion and a visible light source and anIR light source.

According to another aspect of the invention, the electric circuitry isconfigured to process the input current from the socket and, basedthereon, operate in either a civilian, visible mode or a covert IR mode.Where the current is in one electrical state, such as for example acertain voltage, the electric circuit sends power to the visible lightsource. When the current is in a different electrical state, e.g., adifferent voltage level, the circuitry sends power only to the IRsource, and no visible light is emitted. The electrical states of thecurrent may be any variation of electrical parameters thereof, includingamperage, voltage, frequency, or data encoded therein, etc.

Such a system allows for ready upgrade of existing aircraft because allcontrol may be accomplished over a single pair of wires, as are alreadyin existing systems that do not have IR mode capability. To upgrade,light source units according to the invention are simply inserted intothe existing navigational light sockets.

Other objects and advantages of the invention will become apparent fromthe specification herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic top view of an aircraft graphicallyillustrating one of the placements for a navigational light and showingthe required light intensity in varying angles, as required by the FAA.

FIG. 2 shows a side view of the dual mode light source unit of thepresent invention.

FIG. 3 shows a front view of the LED mounting board used in the unit,showing the arrangement of the LEDs and the IR emitter thereon before itis flexed into position in the unit.

FIG. 4 is a graphical illustration of the operation of a typicalinstallation of the dual mode unit of the invention.

FIG. 5 is a functional diagram of the electronic circuitry of the dualmode light source unit.

FIG. 6 is a more detailed schematic of the circuitry of the dual modelight source unit.

FIG. 7 is a horizontal cross-sectional view through an aircraft wingtip,showing a conventional incandescent bulb fixture and glass lens of theprior art.

FIG. 8 is a schematic illustration of an upgrade to an aircraft lightingsystem with another embodiment of light source module according to thepresent invention.

FIG. 9 is a horizontal cross-sectional view of a wingtip having anupgraded aircraft lighting system with embodiment of light source moduleshown in FIG. 8.

FIG. 10 is a plan view of a preferred embodiment of a modular aircraftlight unit.

FIG. 11 is a side view of the aircraft light unit of FIG. 10.

FIG. 12 is a partially cut-away view as in FIG. 11 showing the interiorof the aircraft light unit.

FIG. 13 is a perspective view of the bottom of the metallic outerportion of the modular unit of FIGS. 10 to 12.

FIG. 14 is a perspective view of an aircraft light unit as shown inFIGS. 10 to 13 installed in an aircraft wingtip.

FIG. 15 is a perspective illustration of the relative position of theinfra red emitter and a reflector plate in the aircraft light unit ofFIGS. 10 to 14.

FIG. 16 is a chart showing the relative visible and covert emissionsfrom a device according to the invention for the settings of thefive-position navigational light intensity switch in an F-15 cockpitcontrol panel.

DETAILED DESCRIPTION

Referring to FIG. 1, all aircraft flying in civilian airspace arerequired to be equipped with visible navigational lights to allow themto see each other at night or in conditions of bad visibility. The FAAhas defined the parameters for acceptable navigational light intensitybased on the angle of viewing thereof. A navigational light on top of anaircraft must project at least 40 candelas luminous intensity directlyahead, i.e. zero degrees, and in a 10-degree angular spread to the sideof the plane. Between 10 and 20 degrees off the nose of the plane, 30candelas luminous intensity are required. Between 20 and 110 degrees, anillumination of only 5 candelas is required.

Military aircraft are also required to have such visible navigationlighting systems for operation in civilian areas in a non-covert,visible mode. Accordingly, even military aircraft are equipped with anumber of navigational lights, which have traditionally been a pluralityof incandescent bulbs. For each bulb, the aircraft has an electric bulbsocket, usually the type of socket that is referred to as a bayonetsocket, which is wired into the aircraft's electrical system. The socketis configured to receive and secure a bulb therein and make anelectrical contact with it. Power from the electronic system of theaircraft is then supplied through the socket. The incandescent bulbnavigation lights of the prior art are conventionally powered byelectricity from the internal electronics of the aircraft, which in mostU.S. fighter aircraft is 400 Hz AC at 115 volts with a single doublewire running to each light bulb.

Normally, the pilot has a brightness control dial or similar controldevice in the cockpit that allows him to adjust the brightness of theexternal navigational lights up or down. Adjusting this control dial inprior art systems changes the voltage of the 400 Hz AC current sent tothe bulb over the plane's internal electrical wiring.

As best seen in FIG. 2, the dual mode light source unit 3 for a militaryaircraft comprises a connection portion 5 which is preferably a standardsingle-contact bayonet base, which is configured to fit in and connectwith a standard bayonet socket for an incandescent bulb in the aircraft.When secured in the bayonet socket, connection portion 5 makes thenecessary contacts and receives the control current from the aircraftelectrical system in the same way as the incandescent bulbs of the priorart.

The electrical current received is transmitted to electronic circuitryin the form of circuit board 7 mounted fixedly on connection portion 5and double-sided copper circuit board 9 fixedly attached to circuitboard 7 and extending upwardly therefrom. Connected with both boards 7and 9 is light source mounting board 11, made of thin flex circuit boardand supporting the light emitting components of the unit.

As best seen in FIG. 3, the thin flex board 11 has an array ofcomponents secured thereto. The board 11 supports a visible light sourcein the form of thirty-four (34) visible light-emitting diodes 13 or LEDs(3500 MCD) mounted thereon, in two 4×4 arrays and one on either side ofIR light source 15. These LEDs 13 are wired in parallel and connected toboard 7 to receive power therefrom, as is IR source 15. A differentnumber of LEDs may be used as required, and also, alternatively, otherarray configurations may be used to achieve the required luminousintensity distribution as well, especially if LEDs specified in thepreferred embodiment are used.

The near-infrared emitter 15 is preferably an emitter such as the superhigh-power GaAlAs IR emitter sold as model no. OD-50W by the Opto DiodeCorp., of Newbury Park, Calif. The preferred IR emitter generates IR ata range of wavelengths centered at about 880 nm, and with a fairly wideangular spread, necessitating only a single emitter for each unit.However, more than one IR emitter may be used, optionally supported inseveral orientations relative to each other. Night vision goggles usedin covert operations are particularly sensitive to the deep red andnear-infrared region of the spectrum, and friendly military equippedwith night vision goggles are readily able to see the IR produced by theIR emitter 15. Without appropriate night vision equipment, however, theIR light is impossible to see.

The LEDs are selected and configured to emit light conforming to FAAluminous intensity requirements, angular coverage requirements, andchromaticity requirements for Aviation Red or Aviation Green. All of theLEDs for a given light unit are either red or green, depending onwhether the unit is to be installed on the left-hand (red) or theright-hand (green) side of the aircraft. The LEDs are high intensitydirectional LEDs, such as those manufactured by Purdy Electronics ofSunnyvale, Calif., with Model number AND180HSP, Motorola, Inc., withModel number HSMC-S690, or Nichia Corporation of Japan as model numberNSPG-510S, or equivalent products. LEDs of this type generally projectfairly intense light only within a cone of about 10 to 15 degrees. Tomeet the FAA requirement for an angular spread of luminous intensitylevels as shown in FIG. 1, the board is bowed, as seen in FIG. 2, sothat the LEDs point in a plurality of angled directions and achieve theluminous intensity distribution required.

The LEDs generate visible light, but unlike incandescent lights, whichare copious emitters of near-infrared energy at any brightness setting,the LEDs are selected for having spectral emission characteristics suchthat they do not generate much, if any, infrared light. As aconsequence, these LEDs will not overpower or unduly degrade anintensified image of the LED when viewed at close range using nightvision goggles.

The dual mode light source is configured to be installed by simplysubstituting the dual mode light source unit for an existing navigationlight bulb. The shape, volume, power requirements, and external physicalconfiguration of the dual mode unit of the disclosed embodiment aresubstantially the same as for the Grimes type 72914/11631, a 6.2-volt,40-watt incandescent bulb. It will be understood however that virtuallyany type of light source might be replaced by a suitably configured dualmode light source unit according to the invention.

The electronics of the dual mode unit are preferably set up to interfacewith the electronic current supplied by the aircraft electrical systemso that no further modification is necessary, and covert mode or visiblemode may be selected by the pilot by the dimmer control already presentfor the navigational lights.

In most current navigation light systems which provide for adjusting thebrightness of the navigation lights, the control of the brightness iseffectuated by varying the voltage of the AC power current sent to thelight between a minimum value of about five volts and a maximum value ofabout 115 volts. According to an aspect of the present invention, thisvarying voltage control is used to give a pilot control over whether theaircraft is operating in visible civilian mode, or covert IR mode.

FIG. 4 illustrates the functionality of the electronic circuitry 7 ofthe unit 3. The circuitry analyses the incoming current from theaircraft, and if the voltage exceeds a preselected threshold voltageV_(threshold), the dual mode unit is placed in visible mode, and onlythe visible LEDs are illuminated. No power is sent to the IR lightsource. The intensity of the visible LEDs remains constant irrespectiveof any changes to different voltages in this range of voltages A.

To enter covert mode, the pilot needs only to turn the existingnavigation light brightness control down low enough, thereby reducingthe input voltage to the unit. When the unit's electronics detect thatthe input voltage has dropped below the threshold voltage, the dual modeunit shifts to covert mode; all power is cut to the visible light source(the LEDs 13), and power is sent to illuminate the IR light source.

The IR light source is fed a constant level of power over the entirerange B of voltages from V_(min) to the threshold voltage. However, itis desirable, where a number of aircraft are flying covert mode andviewing each other's IR emissions through their night vision goggles,that the IR have a distinctive appearance for some or all of theaircraft. This can be accomplished in the present system by causing theIR light source to pulse on and off periodically so that individualaircraft will have a recognizable cycle or “blink rate” to the pulse oftheir IR. Adjustment of the voltage by the pilot in this voltage range Bresults in adjustment of the periodic frequency of the pulsing of the IRemission on the aircraft. Higher voltages result in faster pulsing, andreducing the input voltage slows down the IR pulsing rate. The pulse ispreferably a square wave, and in the preferred embodiment the squarewave keeps the IR source on about 75% of the time.

The operation of the electronic circuitry of the dual mode unit isillustrated best in FIG. 5. The schematic of FIG. 6 parallels FIG. 5,but shows the individual components in greater detail. Equivalent partsare indicated by the same reference number in the figures.

The input AC power current is introduced from the socket connector basethrough line 17, which feeds the current into rectifier doubler 19,which converts the AC to equivalent voltage DC current. This DC currentis delivered to the visual light source (LEDs 13) through visual modeswitch 21, to switch mode voltage regulator 23, which converts thevariable voltage current to a steady DC output, and also to voltagecomparator 25, which determines the mode of the unit, and to IR lightsource 15 through switchable control mode timer circuitry 27.

The determination of which mode the unit is to be in is made atcomparator 25, which receives the input voltage along line 28 andcompares this input voltage to a preset reference voltage from line 29from a divider network which corresponds to the threshold voltage forthe change between covert and visible modes. This reference voltage inthe preferred embodiment is about 5.8 volts, although this thresholdvalue could vary considerably. If the input current is in an electricalstate indicating visible mode (e.g., voltage higher than threshold), thecomparator output 31 snaps to low. This low voltage is sent by line 33to switchable timer 27 for the IR light source, and switches it off sono power goes to the IR light source. The low output on line 31 is alsoinverted by inverter 35, and this high output is sent via line 37 toturn on the switching regulator 21, allowing the constant DC current toflow through to the visible light source LEDs 13. The LEDs thus remainat a constant intensity despite any variations in input voltage at thislevel.

If the input current is in an electrical state that indicates covertmode (e.g., voltage below threshold, range B in FIG. 4), then thecomparator 25 produces an output that snaps to high. This high output isinverted by inverter 35 to produce a low signal to the switch moderegulator 21, cutting the flow of power to the visual light source. Atthe same time, the high output on line 31 switches timer 27 on.

When switched on, timer 27 acts as a voltage controlled oscillator, andthe high output 33 applied thereto runs it in an astable mode,oscillating at a frequency based on the voltage applied thereto alongline 41, with higher frequency oscillation produced by higher inputvoltage. This rate of oscillation is in a range that can be seen by thehuman eye, and provides the adjustable blink rate for the IR lightsource based on the pilot-controlled level of input voltage.

The output of the oscillation of the timer goes to a follower 43 andcauses it to switch a 5 volt power supply to the IR light source on andoff responsive thereto. The resulting pulsing current flows to IR source15 and causes it to pulse periodically. Since the rate of pulsing IR isdependent on the input voltage, it can be adjusted by also adjusting theinput current voltage by adjusting the cockpit brightness control in thelower range that corresponds to covert mode.

An existing aircraft with variable brightness control for itsnavigational lights can be upgraded to an infrared covert capability bysubstituting a dual mode light source unit for each of the incandescentnavigation light bulbs thereof. When this is done, existing brightnesscontrols may be used to operate in visual or covert mode as follows.

In normal civilian airspace, the pilot illuminates the navigation lightsby setting the brightness control at a high setting corresponding to avoltage above the threshold at the sockets. When covert operation isdesired, the pilot dials down the brightness control until the visiblenavigation lights go out. If the pilot puts on night vision goggles, hewill see the IR emitters blinking at a certain rate. He can adjust thisrate to be slower by further dialing down the brightness control. Thesettings for specific recognizable pulsing rates may be incorporatedinto the control as desired to aid in coordination of the speed ofpulsing between aircraft.

New aircraft may also be equipped with dual mode light sources accordingto the invention with substantial benefits as well. The dual mode unithas an enhanced lifetime over that of incandescent bulbs, and alsoobtains an advantage over separate visible/IR systems by use of only asingle wire pair for control of both types of light, reducing labor andcost of manufacture, and to a degree, weight of the aircraft.

Another embodiment of the invention is shown in FIGS. 8 and 9, as wellas a method of upgrading an aircraft with an incandescent light fixture.

An existing incandescent light fixture is an aircraft as shown in FIG.7. The aircraft has a body 51, which for illustrative purposes in FIGS.7 and 8 is a wingtip, with a space 53 therein in which a socket 55 issupported. Socket 55 is part of the electrical system of the aircraft,and is supplied with AC power, usually by a single pair of wires, notshown, as discussed previously herein. Incandescent bulb 57 is removablysecured in socket 55 by a bayonet portion 59 thereof.

The body 51 of the aircraft has an aperture therein through which thebulb 57 in space 53 can be accessed. This aperture is closed duringnormal operation of the aircraft by a lens 61 that is held in apertureby security plate 63 that is secured by Allen bolt 65, and also by a lipstructure generally indicated at 67 on the lens 61 that fits inengagement with the aircraft body 51 at the edge of the aperture.

Referring to FIG. 8, an existing incandescent bulb light can be retrofitor upgraded to an LED-based lamp by installation of a self-containedlight assembly or unit 71 in the aperture of the aircraft body 51.Installation involves removal of the Allen bolt 65 and retaining plate63. The lens 61 and bulb 57 are then removed from the socket 55.

Electrical connection portion, or bayonet fitting, 73 of the unit 71 isinserted into socket 55 so as to receive electrical power therefrom andtransmit the power through a flexible electrical umbilical cable 75 thatlinks bayonet fitting 73 to lighting circuitry housed in unit 71. By useof the bayonet connection 73, power for the unit 71 can be drawn fromthe existing electrical system without modification.

The unit 71 includes a housing 75 that holds control circuitry connectedwith a metallic outer housing 77. The outer housing 77 supports a windowor light portion 79 through which visible light can pass. The outerhousing 77 also supports, for military applications, a second window orIR light transmitting portion 81 of material through which infra-redlight can pass for covert mode operations.

The outer portion 77 of the unit 71 exactly duplicates the shape of thepre-existing lens 61, and is configured to fit in the aperture in theaircraft body 51 in place of and mount identically to lens 61. In themethod of FIG. 8, the bayonet fitting is secured and electricallyconnected in the socket 55, and the umbilical cable is coiled and fitinto the space 53. The unit 71 is then placed in the aperture and a lipstructure 83 of the unit 71 interlockingly engages the edge of theaperture, as the lens 61 was held. Plate 63 is then secured with Allenbolt 65 over unit 71, fitting into a recess 85 at a rear edge of theassembly housing 77.

The outer portion 77 and windows 79 and 81 together define an outersurface that is also identical to the outer surface of the lens 61. Theunit 71 thus becomes the lens 61 duplicated in metal, with appropriatewindows or ports flush with and maintaining the preexistent profile ofthe outer surface. By virtue of its exposed profile and shape matchingthat of the original lens, the unit 71 thus does not affect, compromiseor degrade the aerodynamic characteristics of an aircraft in which thelens forms an integral or important part of the airfoil shape and/ordesign.

Referring to FIG. 9, the light module 71 also includes a housing 87 thatextends inwardly of the aircraft body into space 53. Housing 87 supportsinside it light control circuitry, which is preferably voltagediscrimination and control circuitry similar to the circuitry shown inFIGS. 5 and 6, and discussed above. The circuitry is connected withumbilical cable 75 and receives electrical power therefrom. Thecircuitry in housing 87 is connected by wiring to power supply and/orpower conditioning circuitry 88 and to a plurality of visible-light LEDs89 and an infra-red emitter 91. Depending on an electrical condition orparameter, e.g., voltage, of the electrical current received from socket55 and the electrical system of the aircraft, the light controlcircuitry sends power to and illuminates the visible light LEDs 89 orthe IR emitter 91, as with the first embodiment discussed above.

The visible LEDs 89 are preferably high intensity LEDs, and especiallypreferred are LEDs sold by Lumileds Lighting LLC of San Jose, Calif.under the name Luxeon™ Star. Preferably three of these LEDs are used,supported at appropriate angles on mounting portion 93 so that thevisible light emitted from the LEDs is transmitted through window 79 insaid housing 77 and is angularly distributed according to specificpatterns, e.g., FAA requirements. To aid in proper distribution of thelight from the LEDs, a mirror 95 is also provided inside the outerhousing 77.

In addition to replacing the lens, the unit 71 also replaces theinternal incandescent lamp in aircraft red (left), green (right), orwhite (tail) external navigation light fixtures, and therefore must emitlight of the correct color. The LEDs used in the unit in these differentpositions are preferably color LEDs that emit a light of the appropriatecolor for the location of the fixture in the aircraft, i.e., red, greenor white. Since these LEDs have the correct color light output, thewindow 79 may be of clear material, and not a color filter.

The LEDs 89 are mounted on mounting portion 93 so as to readily transmitheat created to the mounting portion 93. This heat must be carried away(heat-sinked), or light emission from the LEDs will decrease. Both themounting portion 93 and the outer housing 77 are of thermally conductivemetal, preferably aluminum, and, to remove the heat, mounting portion 93is connected thermally and mechanically to the metallic outer housing77, which has an adequate surface area to dissipate the heat produced bythe LEDs. The mounting portion 93 and outer housing 77 are preferably acontinuous aluminum structure or connected by a metal-to-metal contactto form a thermal link with a suitable cross sectional area to thedirection of heat flow, such that heat in mounting portion 93 flows tothe outer housing 77 and is dissipated to the external airflow passingover the aircraft body, and the temperatures of the LEDs remain withinan acceptable operating range.

By virtue of the unit 71 substituting for a fixture of lens, theexternal surface of the metal housing 77 is directly exposed to movingairflow, and the unit 71 thus is particularly efficient in radiatingwaste heat internally generated by the circuitry and LEDs containedwithin it. The metal housing 77 also functions as a mounting chassis forthe light control circuitry and the infra-red emitter, which are alsophysically integrated into, heat-sinked, and protected by said housing77. By such means of heat radiation, which is far more efficient than ina structure in which an array of high intensity LEDs is located beneathor behind an existing lens but not directly thermally bonded to a metalsurface exposed to outside airflow, the unit 71 permits higher intensitylight emission from LEDs than otherwise is possible with existing “plugand play” LED substitutes for incandescent lamps. Also, the LEDs usedare smaller physically than the incandescent lamp and can be mountedcloser to the outer glass lens and connected with the metal part of thefixture nearer the outside of the aircraft, reducing the distance heatmust flow to be released outside the aircraft.

As stated above, the illustrative unit 71 of FIGS. 8 and 9 is configuredfor placement in a military aircraft for which infra-red emission isdesired for covert operations. Consequently, the unit 71 includes IRemitter 91 that selectively into IR light through window 81. The IRemitter 91 is preferably surrounded by a shroud 97 that directs all IRemissions in angular directions that can only be seen with NVGs fromdesired aspects, usually upward, above the horizontal horizon of theaircraft.

The light control circuitry for a military aircraft light assembly orunit is preferably dual-mode circuitry, similar to or such as shown inFIGS. 5 and 6. This circuitry receives power from the aircraftelectrical system, preferably through the fixture socket. The electriccircuitry is configured to process the input current from the socket andbased thereon operate in either civilian, visible mode or covert IRmode. Where the current is in one electrical state, such as for exampleat a voltage above a preset threshold, the electric circuit sends powerderived from the incoming current and illuminates the LEDs. When thecurrent is in a different electrical state, e.g., at a voltage below thepreset threshold voltage level, the circuitry cuts power to the LEDs andsends power only to the IR emitter, and no visible light is emitted.

The detected electrical states that are most compatible for interfacewith existing aircraft controls without modification are differentvoltages. Depending on the cockpit electronics, the existing aircraftelectrical system may supply electrical current at any of severalvoltage levels set by the lighting intensity control in the cockpit.Most military aircraft have navigational light dimmer controls in thecockpit with at least two brightness settings, to as many as fivesettings. For example, F-15's usually have a cockpit control switch withfive different illuminations intensity levels producing voltages of,e.g., 30, 50, 70, 90 and 115 volts, while F-16's have only two switchpositions, producing 55 or 110 volts. In either aircraft, however, thelight control circuitry, in the embodiment of FIGS. 5 and 6, detects thedifferent voltage levels using a comparator 25 (FIG. 5), and causes theIR emitter to pulse at different frequencies set by a timer 27 based ondifferent input voltage levels. The different pulsing makes the aircrafteasier to recognize and distinguish from other aircraft by other pilotsusing NVGs.

To make the assembly more adaptable to different aircraft electronics,the light circuitry of the preferred embodiment is modified from thecircuit of FIGS. 5 and 6 in two ways.

First, instead of the comparator 27, the light control circuitry in theunit 71 preferably includes a microcontroller which senses the voltageof the input current supplied from the existing external lightingcontrol located in the cockpit. The microcontroller is pre-programmable(or re-programmable) by a user to respond to different AC or DC voltageinputs from the existing aircraft lighting electrical system and todrive based on the programmed voltage level, driving the visible lightemitting diodes (LEDs) or infrared emitting diodes (IREDs) to emitsteady (constant) output or flashing output of different rates,patterns, duty cycles, etc as desired. Because the voltage valuecorresponding to each given external lighting intensity setting maydiffer slightly from aircraft to aircraft due to tolerances or aging ofaircraft electrical system components, the microcontroller also allowsthe unit to be tailored to individual aircraft and give the same desiredlight output (or infrared output) response for a given intensity settingeven when installed in different aircraft having different electricalcharacteristics.

Second, instead of the timer that adjusts frequency of the flashing IRemitter on the aircraft, the light control circuit is provided with apre-programmable feature through which different flash patterns can beentered and assigned to different voltage levels of current from theaircraft. These flash patterns are used to turn the IR emitter on andoff in time-dependent repeating patterns, which aid in visualidentification of the aircraft with NVGs at a distance. An example ofdifferent flash patterns that might be used in an aircraft such as anF-15 with a five-position intensity control are shown in the chart ofFIG. 16. The flash patterns may be quite varied, but generally arearrangements of short pulses, longer pulses, and intervals of varyingduration between pulses.

Both the setting of the voltage levels for different IR or visibleemissions and the programming of the IR flash patterns are accomplishedby input to the light control circuitry. Preprogramming, orre-programming, of different covert flash characteristics (e.g., simplepulsing at different rates or more complicated patters for flashing,such as a short flash followed by a long flash, or irregularly spacedflashes) may be accomplished on the ground by a user by means of ahand-held programming device that interfaces with programmable circuitryin the unit. The hand-held programming device can input commands, dataand selections of the flash patterns or the electrical states orcharacteristics, such as voltage levels, on which the circuitry makes adetermination of which mode the unit should operate in. The input fromthe hand-held programming device may be accomplished even afterinstallation directly through the window and through an infra-red dataport 99, best shown in FIG. 9, or by a jack or a pin connection on thehousing 87 that can be accessed before the unit 71 is installed, by amechanical plug-in connector from a hand-held device. The circuit can bereprogrammed if necessary to set specific voltage levels or ranges to bedetected, and to set the specific visible or covert emissions andpatterns associated with each of the defined voltage levels or ranges.

It will be understood by those of skill in the art that differentcharacteristics of the current, e.g., amperage or digital data in thecurrent, may also be used to detect from the input current at the socketthe desired covert or visible action, and that the light controlcircuitry may be programmed to modify those parameters and actions asdesired.

For civilian or commercial aircraft, the light unit 71 is built to emitlight energy only in the visible part of the electromagnetic spectrum,and the unit is a self-contained assembly that contains high intensityLEDs that emit visible light, and associated voltage conditioningcircuitry. No separate IR emitter 91 or IR window 81 is supplied in thecivilian version of the unit, but the general form of the housingcopying the external shape of the original lens and being conformal tothe shape of the contour of the aircraft is similar to the militarylight unit.

Since there is no need to selectively control infra-red covert lightingin a civilian aircraft, the light control circuitry functions mainly tocondition the electricity received from the aircraft electronics to beused to directly power the LEDs. Even though configured to emit visiblelight only, however, a commercial aircraft assembly nonetheless benefitsfrom the heat transfer to direct exposure of the metal housing toexternal airflow to facilitate the liberation or radiation of heat fromthe high-intensity visible-light LEDs contained within the housing, thuspermitting greater luminous intensity output from said LEDs cluster thanotherwise would be possible. The LEDs in a civilian version aretherefore also thermally bonded to a mounting portion 93 that isconnected thermally and mechanically to the outer portion 77 of the unit71.

The most preferred embodiment of the light source unit of the inventionis shown in FIG. 10. The light source module 101 of this embodiment isconfigured to have an external shape identical to that of level 61 andsecurement plate 63 combined. As best seen in FIG. 10, the light sourceunit 101 has a metallic outer portion 103 that serves as a frame thatsupports therein a window or light transmissive member 105. Outerportion 103 has a bore 107 therein configured to receive Allen bolt 65therethrough securing the unit 101 in the aperture on the aircraft. Unit103 also has a lip structure 109 that engages the edge of the apertureto hold the unit 101 on the aircraft body 51.

As best seen in FIGS. 11 and 12, below the outer portion 103, the unit101 has an inward housing or electronics envelope 111 that containslight control circuitry as described for any of the precedingembodiments, connected by a flexible electrical umbilical cable 115 witha bayonet fitting 113, which connects with the socket 55 connecting towiring in the aircraft that connects with pilot interface circuitry(e.g., cockpit controls) and receives electrical current therefrom, asdiscussed with respect to the earlier embodiments. The light controlcircuitry is similar to the light control circuitry of the precedingembodiments, especially the programmable form above with the relevantinput port or pins, and it receives the electrical current from theaircraft and selectively transmits power derived therefrom to connectingwiring (not shown) leading to visible-light LED sources or a nearinfra-red emitter.

The LEDs on the unit 101 preferably are three Luxeon™ Star LEDs ofappropriate color and intensity to produce illumination satisfying theFAA or other applicable regulations. These LEDs have an aluminum corethat is a built-in heat sink that can be engaged against a suitablesurface to transmit heat thereto. Two LEDs 117 are each securedthermally and mechanically on mounting structure 119 on a thermallyconductive inclined surface thereof, facing forward and outward of theunit 101 at respective angles to achieve the desired distribution ofvisible light therefrom. The third LED is housed in a prismatic lensstructure 121, but is also mechanically and thermally bonded to a faceof mounting structure 119. The positions of LEDs 117 and lens structure121 distribute the visible light from the LEDs so as to achieve therequisite angular and intensity distribution.

Mounting structure 119 is itself mounted on support plate 123 byfastener on bolt 125. Support plate 123 is supported in a continuousmanner by being secured by fasteners or bolts 127 that fixedly attach tothe lower end of interior rib 129 of outer housing 103. Mountingstructure 119, support plate 123, and outer portion 103 each are ofthermally conductive metal, preferably aluminum, and are thermallyconnected with each other with adequate cross-sectional area to thedirection of heat flow such that heat from the LEDs 117 is transferredto mounting structure 119, and then transmitted to support number 123,through interior rib 129 into the metal outer portion 103, which hasadequate surface area to dissipate the heat into the external airflowover the aircraft. The IR emitter and the circuitry of the unit 101 arealso preferably thermally linked to metal outer portion 103 to dissipateany heat therein as well.

The form of the metallic outer portion 103 is best shown in FIG. 13. Theouter portion 103 is preferably formed as one piece of aluminum. Ribs129 are each provided with threaded bores 130 to receive bolts 127securing the face 132 in engagement with the support plate 123 toprovide for a thermal connection and good heat flow between the parts,and at a minimum, adequate heat flow to dissipate enough heat that theLEDs remain in an acceptable range of operating temperatures. The outerportion 103 includes a frame structure 131 that receives therein thematerial of the window 105, where it is secured by adhesive or otherwiseand preferably caulked in place. The window 105 itself is symmetricaland the frame structure 131 has an aperture therein for receiving andsecuring the window 105 that is symmetrical in terms of the shape ofwindow 105 that it can receive. As a result, the same window 105 can beused with the outer portion 103 on either side of the plane, even thoughthe outer portions 103 from opposite sides of the plane are mirrorimages of each other.

The unit also includes infrared emitter 133 supported on plate 135,which is preferably a printed circuit board that is linked thermally tosink heat to the outer portion 103. The near-infrared emitter 133 ispreferably an emitter such as the super high-power GaAlAs IR emittersold as model no. OD-50W by the Opto Diode Corp., of Newbury Park,Calif. The preferred IR emitter generates IR at a range of wavelengthscentered at about 880 nm, and with a fairly wide angular spread,necessitating only a single emitter for each unit. However, more thanone IR emitter may be used, optionally supported in several orientationsrelative to each other. Plate 135 is preferably also thermally linked tothe metal outer surface of the unit 101 to dissipate heat in the IRemitter 137 to the outside airflow.

It is desirable that infra-red radiation be directed only upwardly fromthe source to be visible with NVGs from other aircraft that are levelwith or above the aircraft with the light unit installed, and to preventviewing of the aircraft from below with NVGs. When the unit 101 isinstalled in an aircraft (see FIG. 14) the IR emitter 133 is actuallyoriented to face downwardly. To prevent IR emissions from radiatingdownwardly, a reflector 137 is provided. This reflector has roughlyhat-shaped cross section and reflects all IR from the emitter upwardly.The spatial relationship of the reflector 137 and the IR emitter isillustrated schematically in FIG. 15.

IR radiation downward is also blocked by IR opaque paint or foil mask139 on the inside of part of the window 105 where it does not obstructdesired visible light from the LEDs when they are illuminated. The mask139 shown in FIG. 14 is partially cut-away to show the IR emitter 133,but normally, the IR emitter 133 would not be visible from the angle ofthe view of FIG. 14. The mask 139 in fact extends upward to whateverheight and whatever shape is necessary to block downward radiation ofthe infra red light.

The window 105 is preferably otherwise of transparent material,especially glass, that transmits therethrough both visible light fromthe LEDs and infra-red radiation from the emitter 137 withoutsubstantial diffusion. In addition, the window is preferably providedwith an electromagnetic interference (EMI) shield to reduce or eliminateemission of susceptibility to radio frequency energy, and with ametallic coating or sieve to create a conductive skin on the unit 101that is less affected by various RF radiation.

Installation of the unit 101 is similar to the method of FIG. 9, and theunit functions as a plug-and-play heat sinked module foe the LEDs andother parts of the unit 101 without the need to structurally tie in withany other structure of the aircraft. The existing lens 61 and securingplate 63 are removed. The bayonet fitting 113 of the unit 101 is placedin the socket 55, and the unit 101 is then secured in the aperture inplace of lens 61 and plate 63. The Allen bolt 65 is re-used to securethe unit 101 to the aircraft body 51 through aperture 107. The apparatusis then ready for use.

The civilian or commercial aircraft variation of the unit 101 does nothave the IR emitter 133 or retroreflector 137. Accordingly, the window105 can be reduced in size to cover the portion of the interior of theunit 101 that emits infra-red light in the military version. Thisincreases the metal surface area of metal outer portion 103, which is anadded benefit because it improves the dissipation of heat created by theLEDs 117.

As with the previous embodiment, the light control circuitry in a unit101 for civilian use is greatly simplified because there is no need forthe unit to screen the input current for possible indications of variouscovert IR mode actions. The circuitry rather primarily functions asvoltage conditioning circuitry, i.e., to convert the input current to aform of electrical power, e.g., lower voltage DC current, that can beapplied to power the LEDs 117.

Whether applied to civilian or military applications, the subjectinvention provides benefits in terms of direct exposure of the metalhousing to external airflow to facilitate the liberation or radiation ofheat from one or more high intensity visible light LEDs contained withinthe housing, thus permitting greater luminous intensity output from theLEDs than otherwise would be possible, and this heat sinking is achievedin a plug-and-play application without need for metal surgery on theaircraft. The commercial and military versions of the light unit affordsubstantial advantages, including:

i. The cost of the system and method of the invention is comparativelylower than that of previous approaches.

ii. Implementation requires no change to existing voltage or powercharacteristics in the aircraft, nor modifications to any part of theexisting aircraft electrical system.

iii. Implementation is quickly accomplished through simple substitutionof the device for existing lenses and lamps.

iv. By virtue of its direct exposure to the air stream, the lightassembly provides improved radiation of internally generated waste heatcompared to previous approaches, thus allowing the LEDs containedtherein to operate at greater efficiency and thus provide greaterluminous intensity for a given physical size.

v. When installed, the exterior shape or profile of the inventionmatches that of existing light fixture lenses, thus causing no change inairfoil and/or aerodynamic characteristics of an aircraft on which it isinstalled.

vi. Covert emissions are visible only from locations level with andabove the aircraft, and different selectable flash characteristics incovert mode facilitate recognition of different aircraft with NVGs atlong ranges, without modification of the aircraft electrical system.

vii. Preprogramming of appropriate voltage levels allows adaptation ofthe light unit to different aircraft electronics, and also allowsmultiple different covert infra-red flash characteristics to be set upin the unit before used using a hand-held programming tool.

The light assembly is not limited to any single particular shape orsize, and its shape, profile and/or configuration may be tailored tomatch virtually any existing lens and interface with virtually anyexisting exterior lighting fixture configuration. Lenses on existingexternal light fixtures typically are secured by at most three screws,and the lamp within said fixtures typically is mounted via a simpletwist-lock bayonet base shown in the embodiments herein, so through thesimple expedient of its substitution for the existing lenses and lamps,the invention provides implementation of visible-only or dual modelighting for aircraft requiring such external lighting more rapidly andat less expense than any other known approach, using the existingfixtures if desired.

An assembly according to the invention also may be implemented as a ‘newstart’ design for exterior light fixtures, where its configuration isoriginal, and it need not duplicate the profile of an existing lens orfit an existing fixture. In whatever the application, however, the lightassembly according to the invention preferably has an outer surface thatis conformal to the outer contour of the aircraft body on at least oneedge, e.g., the leading edge of the assembly meaning that the outersurface of the assembly smoothly merges without substantial interruptionor discontinuity into the contour of the outer surface of the aircraftbody adjacent thereto.

An additional way to reduce the heat from the LEDs (or the arrays ofLEDs) while maintaining an adequate brightness standard is accomplishedusing a brightness enhancement effect produced by flashing. All of theLEDs of the fixture are flashed on and off together at a rate of 10 HZto 20 Hz, and most preferably at a rate of 12 to 15 Hz so as to producethe psycho-optical effect known as brightness enhancement, which makes ahuman see such flashing lights as brighter than if they were on 100% ofthe time. Since the LEDs produce no heat for the portion of the cycleduring which they are off, this reduces the amount of heat that must bedissipated, while providing a perceptibly similar level of brightness.

It will be understood that the invention herein extends well beyond theembodiments of the disclosure, and the terms used in this specificationshould be understood to be language of description, not limitation, asthose of skill in the art with this specification before them will beable to make changes and modifications therein without departing fromthe scope of the invention.

1. A dual mode light unit for an aircraft, said unit comprising: lightcontrol circuitry configured to be operatively connected with wiringconnecting with pilot interface circuitry so as to receive an electricalcurrent therefrom, a visible navigational light source connected withthe light control circuitry, and an infrared light source connected withthe light control circuitry, said light control circuitry, when theelectrical current is in a first electrical state, supplying power tothe visible navigational light source and, when the electrical currentis in a second state, causing the visible light source to producesubstantially no visible light and supplying power to the infrared lightsource so that the infrared light source pulses in a first timedependent pattern, and said pattern having pulses or intervals betweenpulses of two or more different durations.
 2. The dual mode light unitof claim 1 wherein the aircraft wiring includes a socket and the unitincludes a connector base structure configured to be received in thesocket on the aircraft and to receive the electric current through thesocket.
 3. A method of providing an infrared light source to an aircrafthaving a navigational light connected with an electrical systemsupplying electric current thereto, the current being in one of aplurality of electrical states, and the aircraft having apilot-accessible control therein responsive to which the pilot canselectively cause the current to change to a different electrical statefor adjusting brightness of the navigation light, said methodcomprising: removing the navigational light from the aircraft; andinserting in said socket a dual mode light unit according to claim
 2. 4.The dual mode light unit of claim 1 wherein the light control circuitryis configured to receive current having a varying voltage, said firstand second electrical states of the current being first and secondvoltages thereof.
 5. A method of providing an infrared light source toan aircraft having a navigational light connected with an electricalsystem supplying electric current thereto, the current being in one of aplurality of electrical states, and the aircraft having apilot-accessible control therein responsive to which the pilot canselectively cause the current to change to a different electrical statefor adjusting brightness of the navigation light, said methodcomprising: removing the navigational light from the aircraft; andinserting in said socket a dual mode light unit according to claim
 4. 6.The dual mode light unit of claim 4 wherein the light control circuitryis configured to receive AC current having a varying voltage.
 7. Amethod of providing an infrared light source to an aircraft having anavigational light connected with an electrical system supplyingelectric current thereto, the current being in one of a plurality ofelectrical states, and the aircraft having a pilot-accessible controltherein responsive to which the pilot can selectively cause the currentto change to a different electrical state for adjusting brightness ofthe navigation light, said method comprising: removing the navigationallight from the aircraft; and inserting in said socket a dual mode lightunit according to claim
 6. 8. The dual mode light unit of claim 1wherein said flash pattern is cyclically repeated.
 9. A method ofproviding an infrared light source to an aircraft having a navigationallight connected with an electrical system supplying electric currentthereto, the current being in one of a plurality of electrical states,and the aircraft having a pilot-accessible control therein responsive towhich the pilot can selectively cause the current to change to adifferent electrical state for adjusting brightness of the navigationlight, said method comprising: removing the navigational light from theaircraft; and inserting in said socket a dual mode light unit accordingto claim
 8. 10. The dual mode light unit of claim 1 wherein the lightcontrol circuitry, responsive to the current being in a third electricalstate, causes the infrared light source to pulse in a second timedependent pattern different from the first pattern.
 11. A method ofproviding an infrared light source to an aircraft having a navigationallight connected with an electrical system supplying electric currentthereto, the current being in one of a plurality of electrical states,and the aircraft having a pilot-accessible control therein responsive towhich the pilot can selectively cause the current to change to adifferent electrical state for adjusting brightness of the navigationlight, said method comprising: removing the navigational light from theaircraft; and inserting in said socket a dual mode light unit accordingto claim
 10. 12. The dual mode light unit of claim 10 wherein the lightcontrol circuitry is configured to receive current having a varyingvoltage, said first, second, and third electrical states of the currentbeing respective voltages thereof.
 13. A method of providing an infraredlight source to an aircraft having a navigational light connected withan electrical system supplying electric current thereto, the currentbeing in one of a plurality of electrical states, and the aircrafthaving a pilot-accessible control therein responsive to which the pilotcan selectively cause the current to change to a different electricalstate for adjusting brightness of the navigation light, said methodcomprising: removing the navigational light from the aircraft; andinserting in said socket a dual mode light unit according to claim 12.14. The dual mode light unit of claim 10 wherein the light controlcircuitry has an input through which a user can program the circuitry toselect or define the flash patterns or to select the electrical statesto which the circuitry responds.
 15. A method of providing an infraredlight source to an aircraft having a navigational light connected withan electrical system supplying electric current thereto, the currentbeing in one of a plurality of electrical states, and the aircrafthaving a pilot-accessible control therein responsive to which the pilotcan selectively cause the current to change to a different electricalstate for adjusting brightness of the navigation light, said methodcomprising: removing the navigational light from the aircraft; andinserting in said socket a dual mode light unit according to claim 14.16. The dual mode light unit of claim 1 wherein said visible lightsource comprises a set of LEDs supported in the unit and connected withthe light control circuitry.
 17. A method of providing an infrared lightsource to an aircraft having a navigational light connected with anelectrical system supplying electric current thereto, the current beingin one of a plurality of electrical states, and the aircraft having apilot-accessible control therein responsive to which the pilot canselectively cause the current to change to a different electrical statefor adjusting brightness of the navigation light, said methodcomprising: removing the navigational light from the aircraft; andinserting in said socket a dual mode light unit according to claim 15.18. The dual mode light unit of claim 16 wherein the light unit isconfigured to be secured in a space in a body of the aircraft, saidlight unit including a metallic portion exposed to external airflow whenin said space, and the LEDs being thermally linked to the metallicportion such that heat generated by the LEDs flows to the metal portionand is dissipated to the airflow such that the LEDs remain attemperatures within an operational temperature range thereof.
 19. Amethod of providing an infrared light source to an aircraft having anavigational light connected with an electrical system supplyingelectric current thereto, the current being in one of a plurality ofelectrical states, and the aircraft having a pilot-accessible controltherein responsive to which the pilot can selectively cause the currentto change to a different electrical state for adjusting brightness ofthe navigation light, said method comprising: removing the navigationallight from the aircraft; and inserting in said socket a dual mode lightunit according to claim
 18. 20. The dual mode light unit of claim 18wherein the metallic portion supports a window member through whichlight from the LEDs can pass, said window and metallic portion closingsaid space against said external airflow over the aircraft body.
 21. Thedual mode light unit of claim 20, wherein the light control circuitryilluminates the LEDs by supplying to said LEDs an electrical powercurrent derived from the electrical current received from the aircraftelectrical system.
 22. A method of providing an infrared light source toan aircraft having a navigational light connected with an electricalsystem supplying electric current thereto, the current being in one of aplurality of electrical states, and the aircraft having apilot-accessible control therein responsive to which the pilot canselectively cause the current to change to a different electrical statefor adjusting brightness of the navigation light, said methodcomprising: removing the navigational light from the aircraft; andinserting in said socket a dual mode light unit according to claim 21.23. The dual mode light unit of claim 20 wherein said window andmetallic portion define an outer surface that is conformal to an outercontour of the aircraft body.
 24. A method of providing an infraredlight source to an aircraft having a navigational light connected withan electrical system supplying electric current thereto, the currentbeing in one of a plurality of electrical states, and the aircrafthaving a pilot-accessible control therein responsive to which the pilotcan selectively cause the current to change to a different electricalstate for adjusting brightness of the navigation light, said methodcomprising: removing the navigational light from the aircraft; andinserting in said socket a dual mode light unit according to claim 23.25. The dual mode light unit of claim 20 wherein said metallic portionand the window form a structure that has an engagement structureengaging the aircraft body for securing the unit in said space and thatemulates an engagement portion and outer contour of a lens used to coverthe space when an incandescent light source is used for in the space asthe navigational light source.
 26. A method of providing an infraredlight source to an aircraft having a navigational light connected withan electrical system supplying electric current thereto, the currentbeing in one of a plurality of electrical states, and the aircrafthaving a pilot-accessible control therein responsive to which the pilotcan selectively cause the current to change to a different electricalstate for adjusting brightness of the navigation light, said methodcomprising: removing the navigational light from the aircraft; andinserting in said socket a dual mode light unit according to claim 25.27. The dual mode light unit of claim 20 wherein said metallic portionand the window form a structure that has an engagement structureengaging the aircraft body for securing the unit in said space and thatemulates an engagement portion and outer contour of a lens used to coverthe space when an incandescent light source is used for in the space asthe navigational light source together with a securement member thatsecures the lens in position over said space.
 28. A method of providingan infrared light source to an aircraft having a navigational lightconnected with an electrical system supplying electric current thereto,the current being in one of a plurality of electrical states, and theaircraft having a pilot-accessible control therein responsive to whichthe pilot can selectively cause the current to change to a differentelectrical state for adjusting brightness of the navigation light, saidmethod comprising: removing the navigational light from the aircraft;and inserting in said socket a dual mode light unit according to claim27.
 29. The dual mode light unit of claim 20 wherein said metallicportion includes a frame structure in which the window is securinglyretained.
 30. The dual mode light unit of claim 29 wherein said windowis symmetrical and the frame structure receives the window in asymmetrical aperture therein.
 31. A method of providing an infraredlight source to an aircraft having a navigational light connected withan electrical system supplying electric current thereto, the currentbeing in one of a plurality of electrical states, and the aircrafthaving a pilot-accessible control therein responsive to which the pilotcan selectively cause the current to change to a different electricalstate for adjusting brightness of the navigation light, said methodcomprising: removing the navigational light from the aircraft; andinserting in said socket a dual mode light unit according to claim 30.32. A method of providing an infrared light source to an aircraft havinga navigational light connected with an electrical system supplyingelectric current thereto, the current being in one of a plurality ofelectrical states, and the aircraft having a pilot-accessible controltherein responsive to which the pilot can selectively cause the currentto change to a different electrical state for adjusting brightness ofthe navigation light, said method comprising: removing the navigationallight from the aircraft; and inserting in said socket a dual mode lightunit according to claim
 29. 33. A method of providing an infrared lightsource to an aircraft having a navigational light connected with anelectrical system supplying electric current thereto, the current beingin one of a plurality of electrical states, and the aircraft having apilot-accessible control therein responsive to which the pilot canselectively cause the current to change to a different electrical statefor adjusting brightness of the navigation light, said methodcomprising: removing the navigational light from the aircraft; andinserting in said socket a dual mode light unit according to claim 20.34. The dual mode light unit of claim 1, and the light control circuitryincluding circuitry detecting whether the current has a voltage that isabove a preselected threshold voltage level, and responsive to such adetection causes the light unit to operate in a visible mode whereinpower is supplied to the visible light source.
 35. A method of providingan infrared light source to an aircraft having a navigational lightconnected with an electrical system supplying electric current thereto,the current being in one of a plurality of electrical states, and theaircraft having a pilot-accessible control therein responsive to whichthe pilot can selectively cause the current to change to a differentelectrical state for adjusting brightness of the navigation light, saidmethod comprising: removing the navigational light from the aircraft;and inserting in said socket a dual mode light unit according to claim34.
 36. The dual mode light unit of claim 1, and the light controlcircuitry, where the current has a voltage that is lower than apreselected threshold voltage level, operating the dual mode light unitin a covert mode wherein the light unit generates no visible light andpower is supplied only to the infrared light source.
 37. The dual modelight unit of claim 36 wherein the light control circuitry has an inputthrough which a user can program the circuitry to define the thresholdvoltage level.
 38. A method of providing an infrared light source to anaircraft having a navigational light connected with an electrical systemsupplying electric current thereto, the current being in one of aplurality of electrical states, and the aircraft having apilot-accessible control therein responsive to which the pilot canselectively cause the current to change to a different electrical statefor adjusting brightness of the navigation light, said methodcomprising: removing the navigational light from the aircraft; andinserting in said socket a dual mode light unit according to claim 37.39. A method of providing an infrared light source to an aircraft havinga navigational light connected with an electrical system supplyingelectric current thereto, the current being in one of a plurality ofelectrical states, and the aircraft having a pilot-accessible controltherein responsive to which the pilot can selectively cause the currentto change to a different electrical state for adjusting brightness ofthe navigation light, said method comprising: removing the navigationallight from the aircraft; and inserting in said socket a dual mode lightunit according to claim
 36. 40. A method of providing an infrared lightsource to an aircraft having a navigational light connected with anelectrical system supplying electric current thereto, the current beingin one of a plurality of electrical states, and the aircraft having apilot-accessible control therein responsive to which the pilot canselectively cause the current to change to a different electrical statefor adjusting brightness of the navigation light, said methodcomprising: removing the navigational light from the aircraft; andinserting in said socket a dual mode light unit according to claim 1.41. The method of claim 40 wherein the navigational light initially isin a socket covered by a lens held in place by a securement platefastened to the body of the aircraft and overlying the lens, said dualmode light unit having a configuration that emulates the shape of thelens, the method further comprising unfastening the securement platefrom a mounting location thereof on the aircraft body; removing the lensfrom a mounting location thereof on the aircraft body; setting the dualmode light unit in the mounting location; and fastening the securementplate over the dual mode light unit.
 42. The method of claim 40 whereinthe navigational light initially is in a socket covered by a lens heldin place by a securement plate fastened to the body of the aircraft andoverlying the lens, said dual mode light unit having a configurationthat emulates the shape of the lens combined with the securement plate,the method further comprising unfastening the securement plate from amounting location thereof on the aircraft body; removing the lens from amounting location thereof on the aircraft body; setting the dual modelight unit in the mounting locations of the securement plate and thelens; and fastening the dual mode light unit in said mounting location.43. The method of claim 42 wherein the securement plate is fastened tothe aircraft body by a bolt extending through a conforming passagetherein, the dual mode light unit having a securement passage thatmatches the conforming passage of the securement plate, and the step offastening the dual mode light unit includes extending the bolt or amatching replacement bolt through the securement passage in said dualmode light unit and fastening the bolt to said aircraft body.
 44. Anaircraft light unit for placement in a space for a navigation light in abody of an aircraft through an opening, said aircraft having anelectrical system supplying an electrical current to a socket in thespace, said light unit comprising: an electrical connector configured tobe received in the socket and to electrically connect therewith so as toreceive said electrical current; circuitry connected with saidelectrical connector and receiving the electrical current therefrom; alight unit housing configured to be supported on the aircraft body inthe space and closing said opening; and at least one visible light LEDsupported in the housing and being connected with the circuitry andreceiving electrical power therefrom so that the LED emits visiblelight; the housing including an outer portion over said opening and overthe LED, said outer portion having a light transmissive member throughwhich the visible light from the LED can pass, and a thermallyconductive metal outer member supporting the light transmissive memberover the LED; said metal outer member and said light transmissive memberdefining an outer surface of the housing that is conformal to a contourof the body of the aircraft; the LED having a thermal link to the metalouter member that carries heat from the LED to the metal outer member,the metal outer member having a metallic outer surface with a surfacearea large enough and the thermal link having sufficient thermalconductivity such that heat from the LED is dissipated into air flowingover the outer portion so as to keep the LED in an operationaltemperature range thereof.
 45. The aircraft light unit of claim 44wherein the electrical connector is a bayonet fixture.
 46. The aircraftlight unit of claim 45 wherein the circuitry is supported in the housingand the bayonet fixture is connected to the circuitry by a flexibleelectrical cable.
 47. A method of installing a navigational light to anaircraft having wiring supplying electric current in one of a pluralityof electrical states to a navigational light on the aircraft, saidmethod comprising: removing the navigational light from the aircraft;and connecting a light unit according to claim 46 to the wiring of saidaircraft.
 48. A method of installing a navigational light to an aircrafthaving wiring supplying electric current in one of a plurality ofelectrical states to a navigational light on the aircraft, said methodcomprising: removing the navigational light from the aircraft; andconnecting a light unit according to claim 45 to the wiring of saidaircraft.
 49. The aircraft light unit of claim 44 wherein the electricalcurrent is alternating current and the circuitry converts thealternating current to DC current at an appropriate voltage for the LEDand transmits the DC current to the LED.
 50. A method of installing anavigational light to an aircraft having wiring supplying electriccurrent in one of a plurality of electrical states to a navigationallight on the aircraft, said method comprising: removing the navigationallight from the aircraft; and connecting a light unit according to claim49 to the wiring of said aircraft.
 51. The aircraft light unit of claim44 wherein the metal outer member has a frame structure that holds thetransmissive member.
 52. The aircraft light unit of claim 51 wherein thetransmissive member is symmetrical across a center plane thereof.
 53. Amethod of installing a navigational light to an aircraft having wiringsupplying electric current in one of a plurality of electrical states toa navigational light on the aircraft, said method comprising: removingthe navigational light from the aircraft; and connecting a light unitaccording to claim 52 to the wiring of said aircraft.
 54. A method ofinstalling a navigational light to an aircraft having wiring supplyingelectric current in one of a plurality of electrical states to anavigational light on the aircraft, said method comprising: removing thenavigational light from the aircraft; and connecting a light unitaccording to claim 51 to the wiring of said aircraft.
 55. The aircraftlight unit of claim 44 wherein the outer surface of the light unitemulates an outer surface of a lens or an outer surface a lens incombination with a securement member used for covering the opening inthe aircraft body when an incandescent bulb is used as a navigationlight in the space.
 56. A method of installing a navigational light toan aircraft having wiring supplying electric current in one of aplurality of electrical states to a navigational light on the aircraft,said method comprising: removing the navigational light from theaircraft; and connecting a light unit according to claim 55 to thewiring of said aircraft.
 57. The aircraft light unit of claim 44 whereinthe thermal link includes a metallic mounting structure on which the LEDis mounted so as to transmit heat thereto, the mounting structureengaging the metal outer member.
 58. A method of installing anavigational light to an aircraft having wiring supplying electriccurrent in one of a plurality of electrical states to a navigationallight on the aircraft, said method comprising: removing the navigationallight from the aircraft; and connecting a light unit according to claim57 to the wiring of said aircraft.
 59. The aircraft light unit of claim57 wherein the mounting structure and the metal outer member are ofaluminum.
 60. A method of installing a navigational light to an aircrafthaving wiring supplying electric current in one of a plurality ofelectrical states to a navigational light on the aircraft, said methodcomprising: removing the navigational light from the aircraft; andconnecting a light unit according to claim 59 to the wiring of saidaircraft.
 61. A method of installing a navigational light to an aircrafthaving wiring supplying electric current in one of a plurality ofelectrical states to a navigational light on the aircraft, said methodcomprising: removing the navigational light from the aircraft; andconnecting a light unit according to claim 44 to the wiring of saidaircraft.
 62. The method of claim 61 wherein the navigational lightinitially is in a socket covered by a lens held in place by a securementplate fastened to the body of the aircraft and overlying the lens, saidlight assembly having a configuration that emulates the shape of thelens, the method further comprising unfastening the securement platefrom a mounting location thereof on the aircraft body; removing the lensfrom a mounting location thereof on the aircraft body; setting theassembly in the mounting location; and fastening the securement plateover the assembly.
 63. The method of claim 61 wherein the aircraftinitially has a navigational light in the socket covered by a lens heldin place by a securement plate fastened to the body of the aircraft andoverlying the lens, said light assembly having a configuration thatemulates the shape of the lens combined with the securement plate, themethod further comprising unfastening the securement plate from amounting location thereof on the aircraft body; removing the lens from amounting location thereof on the aircraft body; setting the assembly inthe mounting locations of the securement plate and the lens; andfastening the assembly in said mounting location.
 64. The method ofclaim 63 wherein the securement plate is fastened to the aircraft bodyby a bolt extending through a conforming passage therein, the assemblyhaving a securement passage that matches the conforming passage of thesecurement plate, and the step of fastening the assembly includesextending the bolt or a matching replacement bolt through the securementpassage in said light assembly and fastening the bolt to said aircraftbody.
 65. The aircraft light unit of claim 44 wherein an infra redemitter is connected with the circuitry, and said circuitry includesdiscriminator circuitry that determines from a characteristic of theelectrical current whether the unit is selected for a visible light modeor a covert IR mode, and illuminates the LED for visible mode, andilluminates the infra red emitter for covert IR mode.
 66. The aircraftlight unit of claim 65 wherein the circuitry has an input through whicha user can program the circuitry to set the characteristic that is usedby the discriminator circuitry.
 67. A method of installing anavigational light to an aircraft having wiring supplying electriccurrent in one of a plurality of electrical states to a navigationallight on the aircraft, said method comprising: removing the navigationallight from the aircraft; and connecting a light unit according to claim66 to the wiring of said aircraft.
 68. A method of installing anavigational light to an aircraft having wiring supplying electriccurrent in one of a plurality of electrical states to a navigationallight on the aircraft, said method comprising: removing the navigationallight from the aircraft; and connecting a light unit according to claim65 to the wiring of said aircraft.
 69. An aircraft light assembly for anaircraft, said aircraft having a body with an outer surface exposed toan external airflow over the aircraft, said aircraft light assemblycomprising: a visible light apparatus configured to be supported on thebody of the aircraft, said apparatus including one or more lightemitting diode devices generating visible light; and an outer structureoverlying the light emitting diode devices, said outer structure havinga light transmissive portion through which visible light from the lightemitting diode devices can pass, and a metallic portion connected withthe light transmissive portion and securing said light transmissiveportion on the aircraft, said metallic portion having an outer surfaceexposed to the external airflow; and the light emitting diode devicesbeing thermally linked to said metallic portion so that heat created inthe light emitting diode devices flows to the outer surface of themetallic portion and is dissipated into the external airflow.
 70. Theaircraft light assembly of claim 69 wherein the aircraft body has edgesdefining an aperture in the outer surface of the aircraft body providingaccess to a space in the body of the aircraft, said visible lightapparatus being configured to be received in said space, and said outerstructure being configured to engage the edges of the aperture on theaircraft body and to cover the aperture and enclose the space.
 71. Amethod of installing navigational lighting on an aircraft having anelectrical system supplying electric current to a navigational light onthe aircraft, said method comprising: removing the navigational lightfrom the aircraft; and connecting a light assembly according to claim 70in place thereof.
 72. The aircraft light assembly of claim 70 whereinsaid outer structure has an outer surface conformal with the outersurface of the aircraft body.
 73. A method of installing navigationallighting on an aircraft having an electrical system supplying electriccurrent to a navigational light on the aircraft, said method comprising:removing the navigational light from the aircraft; and connecting alight assembly according to claim 72 in place thereof.
 74. The aircraftlight assembly of claim 70 wherein said outer structure has an outersurface that duplicates an outer surface of a lens or lens assembly usedto cover said aperture when an incandescent bulb is used as anavigational light in the space.
 75. A method of installing navigationallighting on an aircraft having an electrical system supplying electriccurrent to a navigational light on the aircraft, said method comprising:removing the navigational light from the aircraft; and connecting alight assembly according to claim 74 in place thereof.
 76. The aircraftlight assembly of claim 70 wherein the assembly includes circuitryadapted to receive electrical current from an electrical system of theaircraft, said circuitry conditioning said electrical current andtransmitting electrical power therefrom to the light emitting diodedevices so as to cause illumination thereof.
 77. The aircraft lightassembly of claim 76 wherein the assembly includes an electricalconnector connected with the circuitry and adapted to be secured in asocket in the aircraft electrical system in said space.
 78. A method ofinstalling navigational lighting on an aircraft having an electricalsystem supplying electric current to a navigational light on theaircraft, said method comprising: removing the navigational light fromthe aircraft; and connecting a light assembly according to claim 77 inplace thereof.
 79. A method of installing navigational lighting on anaircraft having an electrical system supplying electric current to anavigational light on the aircraft, said method comprising: removing thenavigational light from the aircraft; and connecting a light assemblyaccording to claim 76 in place thereof.
 80. The aircraft light assemblyof claim 70 wherein the outer structure of the assembly is configured toemulate an outer surface and engagement structure of a lens assemblyused to cover the aperture, the engagement structure of the lensassembly including a securement plate secured overlying a lens thatcovers the aperture when an incandescent bulb is used as a light sourcetherein, and a fastener or bolt engaging and securing the securementplate to the aircraft body, said fastener engaging and securing theouter portion of the aircraft light assembly to the aircraft body wheninstalled thereon.
 81. A method of installing navigational lighting onan aircraft having an electrical system supplying electric current to anavigational light on the aircraft, said method comprising: removing thenavigational light from the aircraft; and connecting a light assemblyaccording to claim 80 in place thereof.
 82. A method of installingnavigational lighting on an aircraft having an electrical systemsupplying electric current to a navigational light on the aircraft, saidmethod comprising: removing the navigational light from the aircraft;and connecting a light assembly according to claim 69 in place thereof.83. The method of claim 80 wherein the navigational light initially isin a socket covered by a lens held in place by a securement platefastened to the body of the aircraft and overlying the lens, said lightassembly having a configuration that emulates the shape of the lens, themethod further comprising unfastening the securement plate from amounting location thereof on the aircraft body; removing the lens from amounting location thereof on the aircraft body; setting the assembly inthe mounting location; and fastening the securement plate over theassembly.
 84. The method of claim 82 wherein the aircraft initially hasa navigational light in the socket covered by a lens held in place by asecurement plate fastened to the body of the aircraft and overlying thelens, said light assembly having a configuration that emulates the shapeof the lens combined with the securement plate, the method furthercomprising unfastening the securement plate from a mounting locationthereof on the aircraft body; removing the lens from a mounting locationthereof on the aircraft body; setting the assembly in the mountinglocations of the securement plate and the lens; and fastening theassembly in said mounting location.
 85. The method of claim 84 whereinthe securement plate is fastened to the aircraft body by a boltextending through a conforming passage therein, the assembly having asecurement passage that matches the conforming passage of the securementplate, and the step of fastening the assembly includes extending thebolt or a matching replacement bolt through the securement passage insaid light assembly and fastening the bolt to said aircraft body.